Mpg123 is a fast, free and portable MPEG audio player and decoder library mainly for Unix (but also ported to other platforms). It supports MPEG 1.0/2.0/2.5 layers 1, 2, and 3, with CD quality playback even on relatively slow CPUs.

cmus is a small, fast, and powerful console music player for Linux and *BSD. It supports almost all common file formats, SHOUTcast/Icecast streaming, and multiple output plugins. cmus features multiple media library views, a playqueue, a directory browser, powerful filters, and vi-style search and keybindings. It also features gapless playback, ReplayGain, Unicode support, and customizable color schemes.

SMPlayer is a complete media player for Windows and Linux. It uses MPlayer as a playback engine, which is capable of playing most video and audio formats (AVI, mkv, WMV, MP4, MPEG, etc.). It can also play and download YouTube videos. One of the most interesting features is that it remembers the settings of all files you play. So if you start to watch a movie but have to leave, when you open that movie again it will resume at the same point you left it, and with the same settings: audio track, subtitles, volume, etc.

Mylene is a command line MPEG audio player. It can
play plain and system embedded MPEG audio streams
and works for Linux OSS and ALSA emulated OSS and
Mac OS X. The player can be used interactively by
telling it to establish a UNIX or INET server on
which commands can be received. It features
sophisticated song selection filters, the ability
to interpret programs written in a C-like
programming language and user formatted text
output among others. The seek-h262 MPEG decoder is
required for audio and system MPEG decoding.